1. Field of the Invention
The present invention relates to electronic devices and systems, and, more particularly, to analog-to-digital converters and systems containing them.
2. Description of the Related Art
Analog-to-digital converters are necessary parts of any system that uses digital techniques to process or analyze real-world electrical data. For example, digital television converts the analog broadcast signal to a digital signal for digital image processing and frame storage. The processed digital signal is then typically converted back to an analog signal for picture tube control. Similarly, video cassette recorders (VCRs) and combination video cameras plus recorders (Camcorders) and digital audio tape systems (DATs) may use digital signal processing after converting analog video signals to digital.
Other analog signals such as those found in hard disk drives, speech, sonar, radar, seismic, electrocardiogram, and mixed analog/digital telecommunications signals may be digitized for processing to extract characteristic parameters, remove noise, cancel echoes, deconvolve, and perform other operations. Fast Fourier transforms and other efficient digital algorithms permit real time processing and demand real time ananlog-to-digital converters. See, generally, Analog-Digital Conversion Handbook (Prentice-Hall 1986) for a discussion of types of analog-to-digital (and digital-to-analog) converters and applications.
However, it is a problem of the known analog-to-digital converters to provide both low power and high speed operation. Converters such as disclosed in U.S. Pat. Nos. 4,803,462 (Hester et al) and 4,831,381 (Hester) use arrays of capacitors. One approach uses CMOS integrated circuit technology and a parallel ("flash") architecture for high speed; see J-T. Wu and B. Wooley, A 100 MHz Pipelined CMOS Comparator for Flash A/D Conversion, IEEE 1988 Custom Integrated Circuits Conference 18.3.1 and A. Yukawa, A CMOS 8-Bit High-Speed A/D Converter IC, 20 IEEE J.Sol.St.Cir. 775 (1985). These approaches have the problem of relatively high power consumption for high enough speed operation.